Reconfigurable switch matrix in particular for space applications

ABSTRACT

The invention relates to a switch matrix having n inlets and p outlets, p being greater n. The matrix includes a plurality of switch members each having one inlet and at least two outlets and each enabling a signal applied to the inlet of said member to be transferred to one of the outlets. Each inlet of the matrix being for connection to one out of r outlets. The switch members are of the electronic type and are mounted in such as manner that when switching is performed consisting in modifying a connection from an inlet of the matrix to an outlet thereof, so that said same inlet is connected to another outlet of the matrix, the losses due to the switch members passed through remain substantially the same value. The invention applies to a matrix enabling a faulty electronic element connected to an outlet of the matrix to be replaced by another element connected to another outlet of the matrix.

The invention relates to a reconfigurable switch matrix in particularfor space applications.

BACKGROUND OF THE INVENTION

For applications that require high reliability, it is common practice toprovide redundant electronic elements so that in the event of one ofthem breaking down, it can be replaced by an identical element. Thisproblem arises in particular for space applications.

To enable a spare element to replace the element that has broken down,it is necessary to provide switching which is controlled eitherautomatically or remotely.

In general, such switching is provided by a matrix having n inlets and poutlets, where the number p of outlets is greater than the number n ofinlets. Each of the inlets delivers a signal to an element connected toa corresponding outlet. Thus, only n out of the p possible outlets arenormally active. When the element connected to one of the outlets breaksdown, then switching is performed so that the corresponding inlet isconnected to an outlet having a replacement element connected thereto.

The switch matrices that have been used in the past make use ofmechanical switches.

An electronic type replacement configuration has yet to be developedthat offers advantages comparable to those of mechanical switchmatrices. Mechanical matrices give rise to negligible attenuation ofabout 0.15 dB, while electronic switches lead to greater losses orattenuation of about 1.5 dB. The greater losses do not, in themselves,constitute an obstacle to the use of electronic switches, since saidelectronic switches make it possible for bulk, mass, and prices to besignificantly lower than the bulk, mass, and prices of matrices havingmechanical type elements. However, it has been found that if eachmechanical switch in a switch matrix of the mechanical type is replacedby an electronic switch, then when switching is performed to replace afaulty element with a spare element, the losses due to the matrix itselfare generally not the same before and after switching.

To remedy that drawback, it is necessary to provide in each sparebranch, a variable gain amplifier enabling the various amounts ofattenuation to be compensated. However, that solution is difficult andexpensive to implement.

OBJECTS AND SUMMARY OF THE INVENTION

To resolve that problem, the switch matrix of the invention includes aplurality of switch members of the electronic type which are mounted insuch a manner that when an inlet of one outlet is switched to anotheroutlet, the losses due to the electronic switch members passed throughremain at substantially the same value.

It is thus not necessary to provide variable gain amplification tocompensate the various losses between the paths passing through in thematrix, since it is the structure proper of said matrix which enablessaid compensation.

In an embodiment, in which each inlet is for connection to r outlets,each inlet is provided with a set of switch members associated so as topresent one inlet and r outlets. In that case, it is preferable toprovide, for each outlet a set of switch members mounted the oppositeway round to the inlet members, said set having r inlets and one outlet;the sets associated with the outlets are preferably of structureanalogous or identical (but symmetrical) to the structure of the setsassociated with the inlets.

The switch members are, for example monolithic microwave integratedcircuit (MMIC) technology switches with two or three outlets andpresenting losses limited to about 1.5 dB.

The present invention provides a switch matrix having n inlets and poutlets, p being greater n, the matrix including a plurality of switchmembers each having one inlet and at least two outlets and each enablinga signal applied to the inlet of said member to be transferred to one ofthe outlets, each inlet of the matrix being for connection to one out ofr outlets. The switch members are of the electronic type and are mountedin such as manner that when switching is performed consisting inmodifying a connection from an inlet of the matrix to an outlet thereof,so that said same inlet is connected to another outlet of the matrix,the losses due to the switch members passed through remain atsubstantially the same value.

In an embodiment, the matrix comprises, for each inlet, a set of switchmembers associated so as to present one inlet and r outlets.

In an embodiment, the matrix comprises, for each outlet, a set of switchmembers having r inlets and one outlet, the sets associated with theoutlets being mounted the opposite way round to the sets associated withthe inlets.

In an embodiment, the sets associated with the outlets are of structureanalogous to the structure of the sets associated with the inlets.

In an embodiment, the electronic switches are microwave range integratedcircuits.

The present invention also provides use of a matrix in replacing afaulty electronic element connected to an outlet of the matrix, withanother element connected to another outlet of the matrix.

BRIEF DESCRIPTION OF THE DRAWING

Other characteristics and advantages of the invention will appear onreading the description of various embodiments, given below withreference to the accompanying drawing, in which:

FIG. 1 is a circuit diagram of a switch member of the invention;

FIG. 2 is a diagram of a switch matrix having a plurality of switchmembers of the invention;

FIG. 3 shows a set or module of switch members of the invention;

FIG. 4 is a figure analogous to that of FIG. 3, but for a variant; and

FIG. 5 shows a switch matrix comprising sets of switch modules of thetype shown in FIG. 3.

MORE DETAILED DESCRIPTION

The switch member 10 shown in FIG. 1 is a switch member comprising a setof transistors that operate at microwave frequencies and made in MMICtechnology, e.g. on a gallium arsenide substrate.

This switch member is for transmitting the signal on the inlet E eitherto the outlet S₁ or to the outlet S₂, but never to both outletssimultaneously. The member 10 comprises firstly two active branches 12and 14, the branch 12 terminating in the outlet S₁ and the branch 14terminating in the outlet S₂. In addition, the member 10 has a shuntbranch 16 enabling the inlet E to be shunted to a load 18, e.g. of 50 Ωin the event of a loss of power to the switches of the member 10.

In the example, each of the branches 12 and 14 has two shunttransistors. Since the branches are identical, it suffices to describeone of them only, specifically the branch 12.

The inlet terminal E is connected to the drain 20 of a transistor 22 bya transmission line 24. The source of the transistor 22 is connected toground.

The terminal 20 is also connected to the outlet S₁ via anothertransmission line 26.

The terminal common to the line 26 and to the outlet S₁ is connected tothe drain 28 of a second transistor 30 whose source is likewiseconnected to ground.

The grids of the two transistors 22 and 30 are both connected to a biasterminal 32 via respective resistors 34 and 36. A DC bias voltage V₁ isapplied to the terminal 32. The terminal common to the resistors 34 and36 is also connected to ground via a resistor 38.

The shunt branch 16 comprises a transistor 40 whose source is connectedto the inlet E and whose drain is connected to one end of the loadresistor 18 whose other end is connected to ground. The grid of thetransistor 40 is connected to a terminal 42 via a resistor 44. The pointcommon to the terminal 42 and to the resistor 44 is connected to groundvia another resistor 46.

A DC bias voltage V₂ is applied to the terminal 42.

Operation is as follows:

When the outlet S₁ is selected, i.e. when the inlet E is to betransferred to the outlet S₁, a voltage V₁ below the pinch-off voltageis applied to the terminal 32 so that each transistor presentspractically infinite resistance; in this example, this voltage is equalto −2 volts. On terminal 42, for biasing the transistor 40 of the shuntbranch 16, a voltage of −2 volts is also applied. Finally, the terminal50 for biasing the transistors of the branch 14 has a voltage V₃ appliedthereto equal to zero volts so that the channels of the transistors areconductive.

Under such conditions, the transistors 22 and 30 of the branch 12constitute open circuits and therefore do not disturb transmission ofthe signal to the outlet S₁.

In contrast, applying zero volts to the terminal 50 of the branch 14causes the corresponding transistors 52 and 54 to act as short circuits.It should be observed that in the microwave range, a short circuit meansthat the signal that is grounded is reflected back to the inlet E and isthus delivered to the outlet S₁.

Applying −2 volts to the terminal 42 for biasing the transistor 40 inthe shunt branch 16 serves to keep this transistor in the open circuitstate.

In the event of a loss of power, i.e. when the bias source(s) apply zerovolts to all of the terminals 32, 42, and 50, or when these terminalsare left disconnected (i.e. open circuit), then the transistors 22 & 30and 52 & 54 in the active branches 12 and 14 are short circuits. Thus,these branches reflect signals back to the inlet E. However, in theevent of such a failure, the transistor 40 presents low resistance andunder such circumstances the signal applied to the inlet E istransferred to the load 18. Thus, electronic elements such as amplifiersand/or filters connected to the outlets S₁ and S₂ do not receive theinput signal. The shunt branch 16 thus provides protection againstlosses of power to the switches.

In a variant, only a single transistor is provided in each active branch12 or 14. Nevertheless, it is preferable to provide two or moretransistors so as to improve shunting to ground when the branch isinactive. The resistance of a “short circuit” transistor is not zero andneeds to be kept within limits.

A switch matrix 60 having twelve inlets E₁ to E₁₂ and sixteen outlets S₁to S₁₆ is described below with reference to FIGS. 2 to 5. This matrixhas a plurality of switch members of the type shown in FIG. 1.

Each inlet can be connected to five of the outlets. Thus, the inlet E₁can be connected to any one of the outlets S₁, S₂, S₃, S₄, and S₅.However, on each occasion, the inlet E₁ is naturally connected to onlyone of those outlets. Similarly, the inlet E₂ can be connected to anyone of the outlets S₂, S₃, S₄, S₅, and S₆, and so on up to the inlet E₁₂which can be connected to any one of the outlets S₁₂, S₁₃, S₁₄, S₁₅,S₁₆. More generally, if the matrix has n inlets and p outlets, then eachinlet can be connected to p-n+1 outlets.

If the inlet E₁ is connected to the outlet S₁ and the inlet E₂ isconnected to the outlet S₄, and if the electronic element (not shown)connected to the outlet S₁ breaks down, it must be possible to replaceit with a redundant element, for example the element connected to theoutlet S₂. Under such conditions, the switch members of the matrix 60are controlled in such a manner as to cause the inlet E₁ to cease to beconnected to the outlet S₁, but instead to be connected to the outletS₂.

Given that a switch member of electronic type presents losses that aresignificantly higher than a mechanical switch member, it is preferableto organize the matrix 60 in such a manner that on each modification tothe connection, there is no modification to the losses. If there were tobe modification to the losses, then it would be necessary to modify thegain of the amplifier that takes over from an amplifier that has brokendown, and that would make implementation of the circuit significantlymore complicated. An electronic member imparts loss of the order of 1.5dB, whereas the corresponding loss for a mechanical switch member is ofthe order of 0.15 dB.

To achieve the objective of maintaining losses in the event of amodification to the connection, the invention provides for switchmembers to be grouped together in sets or modules 62 as shown in FIG. 3or 64 as shown in FIG. 4. In addition, all of the inlets E₁, E₂, etc.are associated with mutually identical sets, and all of the outlets S₁,S₂, etc. are associated with the same sets as explained below withreference to the example shown in FIG. 5.

FIGS. 3 and 4 relate to the case where the switch members can be of twokinds only, namely a first kind with one inlet and two outlets, and asecond kind with one inlet and three outlets (not counting the shuntoutlets). The sets 62 and 64 are intended for use with the example shownin FIG. 2; each of them thus has one inlet and five outlets.

The set 62 shown in FIG. 3 comprises firstly a switch member 10 ₁ havingone inlet 66 ₁ and three outlets 66 ₂, 66 ₃, and 66 ₄, and secondlythree switch members 10 ₂, 10 ₃, and 10 ₄ each having a single inlet andtwo outlets. Given that only five outlets are required, one of theswitch members (10 ₄) has an outlet that is inactivated. The inlet ofthe member 10 ₂ is connected via a conducting line 70 ₂ to the outlet 66₂ of switch member 10 ₁. Similarly, the inlet of switch member 10 ₃ isconnected via a line 70 ₃ to the outlet 66 ₃ of the member 10 ₁.Finally, the inlet of the member 10 ₄ is connected to the outlet 66 ₄ ofthe member 10 ₁ by a conductor line 70 ₄.

The set 64 shown in FIG. 4 comprises firstly a switch member 10′₁ havingone inlet 66′₁ and two outlets 66′₂ and 66′₃, and secondly two switchmembers 10′₂ and 10′₃ each having one inlet and three outlets. Giventhat only five outlets are required in all as in the preceding example,one of the switch members, in this case the member referenced 10′₃, hasan outlet that is inactivated.

The inlet of member 10′₂ is connected to the outlet 66′₂ of the member10′₁ via a conductor line 70′₂ and the inlet of the member 10′₃ isconnected to the outlet 66′₃ of the member 10′₁ via another conductorline 70′₃.

The way a set 62 or 64 operates can be seen from its structure, and fromthe way each of the individual switch members operates as describedabove with reference to FIG. 1. For example, if the inlet 66 ₁ (FIG. 3)of the set 62 is to be connected to the outlet S_(i) of the member 10 ₃,the member 10 ₁ is caused to connect the inlet 66 ₁ to the outlet 66 ₃,and the member 10 ₃ is caused to connect its inlet to the outlet S_(i) .

In the example shown in FIG. 5, provision is made to associate one set62 with each inlet terminal and with each outlet terminal. Thus, theinlet terminal E₁ is associated with a set 62 ₁, the inlet terminal E₂is associated with the set 62 ₂, . . . the outlet terminal S₁ isassociated with the set 62′₁, the outlet terminal S₂ is associated withthe set 62′₂, etc.

Naturally, the sets 62′₁, 62′₂, etc. are connected the opposite wayround to the sets 62 ₁, 62 ₂, etc. More precisely, the members 10″₂,10″₃, 10″₄ of the set 62′₁ comprise two inlets and one outlet, and themember 10″₁ has three inlets and one outlet.

Finally, conductor lines 80 ₁, 80 ₂, 80 ₃, 80 ₄, 80 ⁵ are providedconnecting each of the outlets of the set 62 ₁ to one of the inlets ofthe sets 62′₁, 62′₂, . . . , 62′₅. In other words, the line 80 ₁connects an outlet from the set 62 ₁ to one of the five inlets of theset 62′₁, the line 80 ₂ connects the second outlet of the set 62 ₁ toone of the five inlets of the set 62′₂, etc. It will be observed thatonly one of the inlets of the set 62′₁ is connected to a conductor line,whereas the other sets 62′₂, 62′₃, 62′₄, etc. have a larger number ofconductor lines terminating at their inlets.

Whatever the connections made by the matrix, each time a signal on aninlet E_(i) is applied to an outlet S_(j), it always passes through thesame types of element, specifically a switch member having one inlet andthree outlets, a conductor line, a switch member having one inlet andtwo outlets, another conductor line 80 _(i), a switch member having twoinlets and one outlet, a conductor line, and finally a switch memberhaving three inlets and one outlet. Under such conditions, losses willalways be the same whatever the connection.

A switch matrix fitted with switch members of the invention presentssize and mass that are considerably smaller than the size and mass of amatrix of mechanical switch elements, and this constitutes a decisiveadvantage for space applications. Finally, the price of such a matrixcan be much smaller than the price of a matrix of mechanical switchmembers.

What is claimed is:
 1. A switch matrix having n inlets and p outlets, pbeing greater n, the matrix including a plurality of switch members eachhaving one inlet and at least two outlets and each enabling a signalapplied to the inlet of said member to be transferred to one of the twooutlets, each inlet of the matrix being for connection to one out of routlets, wherein the switch members are microwave range integratedcircuits and are mounted in such a manner that, when switching isperformed consisting of modifying a connection from a first inlet of thematrix to first outlet thereof so that said first inlet is connected toa second outlet of the matrix, each transferred signal passes throughthe same number and type of switch members and circuit elements bothbefore and after switching so that losses due to the switch memberspassed through by the transferred signal remain at substantially thesame value before and after switching.
 2. A matrix according to claim 1,comprising, for each inlet, a set of switch members associated so as topresent one inlet and r outlets.
 3. A matrix according to claim 2,comprising, for each outlet, a set of switch members having r inlets andone outlet, the sets associated with the outlets being mounted theopposite way round to the sets associated with the inlets.
 4. A matrixaccording to claim 3, wherein the sets associated with the outlets areof structure analogous to the structure of the sets associated with theinlets.
 5. Use of a matrix according to claim 1 enabling a faultyelectronic element connected to an outlet of the matrix to be replacedby another element connected to another outlet of the matrix.
 6. Theswitch matrix according to claim 1, wherein said matrix and said switchmembers are free of signal delay elements.